The invention relates to a pressure relief valve with a spring pressure-loaded diaphragm closing body, which in the closed position sealingly engages on a centrally positioned valve seating surface surrounding a first valve opening and whose spring pressure loading determining the sealing pressure takes place by means of a counterpressure body centrally arranged in the vicinity of and over the valve seating surface, which is surrounded by a channel-like valve chamber covered by the diaphragm closing body and provided in the valve housing body and on which on the overpressure side is provided at least one second valve opening.
A pressure relief valve of this type is known from U.S. Pat. No. 5,944,050. This valve is only suitable for relatively low pressures as a result of the nature of the arrangement or mounting of the diaphragm closing body. It also takes up a relatively large construction volume with a correspondingly high thermal inertia, which has a disadvantageous effect e.g. when used in CO2 air conditioning systems.
U.S. Pat. No. 5,413,311 discloses a diaphragm valve, whose counterpressure body operated by a closing piston is surrounded by a ring, which engages on the diaphragm closing body, both in the closed and the opened valve position and by means of which said diaphragm closing body is fixed in the vicinity of its outer circumference. It also forms a stop for the maximum lifting motion of the counterpressure body. Said stop is positioned in such a way that with the valve opened to the maximum the diaphragm closing body has a planar configuration. Consequently when engaged on the valve seating surface it is downwardly outwardly curved in its central area.
FR-A-26 77 425 discloses a diaphragm closing valve, which is intended to have a maximum opening cross-section. For this purpose in the relieved state, the diaphragm closing body is upwardly and outwardly curved away from the plane of its peripheral fixing in plate-like or step-like manner. For closing purposes it is deformed by a closing piston counter to its spring tension in the direction of the valve seating surface. A downward displacement of the valve seating surface away from the fixing plane of the diaphragm closing member increases the spring elastic deformation of the diaphragm closing body necessary for closing purposes. A ring surrounding the closing piston serves both to fix the diaphragm edge and as a boundary casing for the diaphragm closing body, when the latter has its plate-like starting shape in the relieved state with the closing piston raised.
The problem of the invention is to provide a pressure relief valve of the aforementioned type which, in the case of an adequately large opening cross-section and without overloading its diaphragm closing body, is suitable for pressure differences of more than 150 bar between its inflow and outflow sides. According to a preferred embodiment it has a low thermal inertia due to its particularly compact construction and despite the relatively large flow cross-section, so that it can be used with advantage, particularly in areas with pronounced temperature changes, such as e.g. during the cooling and heating operation of a CO2 air conditioning system.
According to the invention the problem is solved in that the counterpressure body placed over the valve seating surface or a counterpressure plate cooperating therewith is surrounded by a diaphragm support ring held on the valve housing and which extends radially outwards from the counterpressure body over the valve chamber to the outer edge of the diaphragm closing body and above the valve chamber has a circumferential recess, whose depth measured perpendicular to the diaphragm closing body determines the maximum deflection of the diaphragm closing body, so that when the valve is completely opened the diaphragm closing body is supported in an area between the valve seating surface and its outer edge.
Embodiments of the invention are described hereinafter relative to the attached drawings, wherein show: